1. Field of the Disclosure
The present invention relates to a resist material, particularly but not exclusively an electron beam resist material, and to a method for forming a finely patterned resist layer on a substrate surface using the resist material.
2. Description of the Related Art
As is well known, the manufacturing process of various kinds of electronic or semiconductor devices such as ICs, LSIs and the like involves a fine patterning of a resist layer on the surface of a substrate material such as a semiconductor silicon wafer. This fine patterning process has traditionally been conducted by the photolithographic method in which the substrate surface is uniformly coated with a positive or negative tone photoresist composition to form a thin layer of the photoresist composition and selectively irradiating with actinic rays (such as ultraviolet light) through a photomask followed by a development treatment to selectively dissolve away the photoresist layer in the areas exposed or unexposed, respectively, to the actinic rays leaving a patterned resist layer on the substrate surface. The thus obtained patterned resist layer is utilized as a mask in the subsequent treatment on the substrate surface such as etching.
The fabrication of structures with dimensions of the order of nanometers is an area of considerable interest since it enables the realization of electronic and optical devices which exploit novel phenomena such as quantum confinement effects and also allows greater component packing density. As a result, the resist layer is required to have an ever increasing fineness which can by accomplished only by using actinic rays having a shorter wavelength than the conventional ultraviolet light. Accordingly, it is now the case that, in place of the conventional ultraviolet light, electron beams (e-beams), excimer laser beams, EUV and X-rays are used as the short-wavelength actinic rays. Needless to say the minimum size obtainable is primarily determined by the performance of the resist material and the wavelength of the actinic rays.
Various materials have been proposed as suitable resist materials. These include organic resinous materials such as methacrylic resin-based, polystyrene-based and novolac resin based materials. In the case of negative tone resists based on polymer crosslinking, there is an inherent resolution limit of about 10 nm, which is the approximate radius of a single polymer molecule.
It is also known to apply a technique called “chemical amplification” to the polymeric resist materials. A chemically amplified resist material is generally a multi-component formulation in which there is a main polymeric component, such as a novolac resin which contributes towards properties such as resistance of the material to etching and its mechanical stability and one or more additional components which impart desired properties to the resist and a sensitizer. By definition, the chemical amplification occurs through a catalytic process involving the sensitizer which results in a single irradiation event causing exposure of multiple resist molecules. In a typical example the resist comprises a polymer and a photoacid generator (PAG) as sensitizer. The PAG releases a proton in the presence of radiation (light or e-beam). This proton then reacts with the polymer to cause it to lose a dissolution inhibiting functional group. In the process, a second proton is generated which can then react with a further molecule. The speed of the reaction can be controlled, for example, by heating the resist film to drive the reaction. After heating, the reacted polymer molecules are soluble in a developer whilst the unreacted polymer is not (i.e. positive tone resist). In this way the sensitivity of the material to actinic radiation is greatly increased, as small numbers of irradiation events give rise to a large number of exposure events.
In other chemical amplification schemes, irradiation results in cross-linking of the exposed resist material, thereby creating a negative tone resist. The polymeric resist material may be self cross-linking or a cross linking molecule may be included. Chemical amplification of polymeric-based resists is disclosed in U.S. Pat. No. 5,968,712, U.S. Pat. No. 5,529,885, U.S. Pat. No. 5,981,139 and U.S. Pat. No. 6,607,870.
Other materials have been investigated as potential resist materials, including low molecular weight organic molecules (Yoshiiwa M, et. al., Appl. Phys. Lett. 69 (1996) 2605) and inorganic substances such as metal fluorides (Fujita J, et. al., Appl. Phys. Lett. 66 (1995) 3064). C60 (fullerene) demonstrates negative tone behaviour, but has low sensitivity (critical dose about 1×10−2 C/cm2). Various methanofullerene derivatives were subsequently shown to be useful e-beam resist materials by the present inventors, Appl. Phys. Lett. volume 72, page 1302 (1998), Appl. Phys. Lett. volume 312, page 469 (1999), Mat. Res. Soc. Symp. Proc. volume 546, page 219 (1999) and U.S. Pat. No. 6,117,617.
The present inventors have also previously reported on the use of certain polysubstituted triphenylene derivatives as electron beam resist materials as exemplified by EP 01159649 and “Polysubstituted Derivatives of triphenylene as High Resolution Electron Beam Resists for Nanolithography”, A. P. G. Robinson, et al, J. Vac. Sci. Tech. B, 18, No. 6, 2730-2736, (2000).
These materials are cast in chloroform, toluene or monochlorobenzene and developed in certain alcohols (positive tone) or monochlorobenzene (negative tone).
It is an object of the present invention in one aspect to provide a novel photoresist material which obviates or mitigates one or more disadvantages associated with prior art resist materials.